San Francisco is justly famous for its many unique charms, like tangy sourdough, impossibly steep hills, dour quarterbacks and so forth. But there is another way this city differs from the rest of the country, and that is its rules of the road. No, not the official state traffic laws. I'm talking about the real rules, the ones that San Franciscans actually follow when they climb behind a wheel.

I first became aware of this parallel, often extralegal set of guidelines when we moved here from Manhattan. For six months, I was still driving like a New Yorker - only to be honked at, cursed at (or worse) for moves that would be completely normal on West 57th Street.

That experience was painful, and it clearly wasn't much fun for the other drivers, either. So to help those who might be new to this city or simply passing through, here is a set of principles I call "The Real Driving Rules of San Francisco." They're distilled from over a dozen years of studying this city's heretofore unwritten code of traffic conduct.

Important caveat: Neither I nor The Chronicle suggest that you actually follow these rules. Many of them are, in fact, quite illegal.

But don't be surprised if other drivers seem to follow the rules, because they do. Think of this list as an underground cousin to the California Driver Handbook, which you have to master to get a driver's license. Knowing San Francisco's unique habits will help you avoid surprises, keep the peace with other drivers, and - I hope - navigate more safely through our city's streets.

Rule 1

All power to the pedestrians

Pedestrians in a crosswalk have the right of way in every U.S. city, but San Franciscans are unique in asserting their right aggressively. Rather than waiting politely for a pause in traffic, many people here stride boldly into the path of oncoming traffic even if that means drivers have to slam on the brakes to stop. (My theory is this stems from an innate sense of entitlement that comes from living in this mild climate, but that's another story.) So when driving in San Francisco and nearby boroughs, especially Berkeley, proceed with caution whenever pedestrians are around.

Rule 2

Beware of bicyclists

The California Driver Handbook says bicyclists must obey the same traffic laws as cars and ride toward the side of the lane when possible to allow motor vehicles to pass. Some cyclists follow these rules. Others do not. So for safety's sake, you should expect each new bicyclist you meet to roll through stop signs, ignore red lights and dart across lanes until proved sane. Be especially wary of any rider wearing a T-shirt that says "Allowed Full Use of Lane."

Rule 3

Gabriel, don't blow your horn

The Driver Handbook also cautions you to sound your horn only to avoid an impending collision or when approaching a blind mountain curve. In fact, while San Franciscans honk less than New Yorkers, they tend to do so at the exact times when the handbook says you shouldn't - like to speed up slow-moving traffic, nag some other driver who goofed, or simply blow off steam.

There are also special occasions during which prolonged honking is, if not exactly welcome, at least tolerated. These include following major sports victories, during riotous celebrations like regular and Chinese New Year, when crossing a newly opened bridge and whenever Colin Kaepernick strings together more than seven words in a row at a press conference. Even on such occasions, though, horns should be blown only when your car is moving and not when you and all your passengers are drunken teenagers - or you will certainly be branded a jerk.

Rule 4

'After you, Alphonse'

When a vehicle in a parking space is entering a lane of traffic, state law says it must yield to cars already in the lane. But in San Francisco, this rule goes out the window if the cars in the lane are halted at a stop sign or red light. In that case, right of way belongs to the parked vehicle, and cars already in the lane must wait for it to pull out before proceeding. The specific car that should yield to the parked vehicle is the first one that is fully behind it (i.e., you do not have to yield if, say, your car is partly abreast the parked car). The same right of way belongs to cars entering from a gas station or driveway. Be careful: I have seen near-accidents happen when some naive out-of-towner is surprised to see a parked car pull suddenly into his path.

Rule 5

The 4-way-stop 2-step

At intersections with four stop signs, the official Driver Handbook says cars should proceed one at a time in the order in which they arrived - and for big San Francisco streets, that rule generally applies. But in residential neighborhoods, where most four-way stops are found, the rule is different. Here, cars should proceed in alternating pairs, with east- and west-bound cars crossing at the same time, followed by north- and south-bound cars, and so forth. When starting this flow, right of way belongs to the pair with a member who arrived at the stop sign before either of the other pair. In the event that one car is making a left turn, the turning car should pause at mid-intersection to allow the straight-driving car to cross before turning.

Rule 6

'Bus lane? What bus lane?'

When driving in downtown San Francisco, you will encounter lanes marked "Bus Only" - and state law warns you to stay out of them unless making a turn. When no buses are present, however, the rule changes. Then it is considered pushy but not totally off-limits to duck into the bus lane for a block or two in order to get around slow-moving traffic, show off your horsepower or for other reasonable purposes. As a courtesy, just slip back into the proper lane every few blocks in order not to be labeled a jerk (see rule 8).

Rule 7

The game of lanes

Driving in New York is a game of position. Lane markers are helpful reminders but should be ignored when inconvenient. If, for example, you need to change lanes but can't get in, you just drive astride the lane marker until your preferred lane opens up. In San Francisco, on the other hand, driving is a game of lanes. You must know where each lane will go several blocks (or miles) ahead and get in the appropriate one now. As a corollary, once in a lane, you should mostly stay there. And so long as drivers around you are not obvious jerks (see Rule 8), it is considered polite to yield to some idiot who signals that he/she wants to enter your lane even if that means delaying everyone behind you. (In New York, by contrast, you should never let anyone into your lane, ever.) There are interesting exceptions to the Game of Lanes rule at busy intersections, like entering the Octavia Street approach to Interstate 80 from Oak Street, where all traffic shifts one lane to the right at the last minute causing a predictably horrible mess. But those are too complicated to explain here.

Rule 8

The Obvious Jerk Exception

The one exception to the above rules - and, indeed, many official traffic laws - comes when you are dealing with an Obvious Jerk. An Obvious Jerk is a person who is rude, arrogant, negligently oblivious or simply ignorant of the finer points of San Francisco driving. (That's what I was during my first six months here.) When another driver does something that identifies him/her as a jerk, this rule says you're free to react any way you want - including swearing, honking, blocking him from your lane, etc. This is especially so if the boorish behavior was witnessed by other nearby drivers.

That last rule may seem harsh. But it's the way San Franciscans teach newbies how to drive here - including these unwritten rules of the road.

Your rules

What are your rules of the road? Kevin McKean is offering his eight rules for San Francisco drivers (all illegal, and all the unofficial rules of roadway conduct). We know you have a few "rules" you've observed too. Send your rules and pithy comments to www.sfgate.com/submissions/#1.

Kevin McKean is both a driver and bicyclist in San Francisco who promises not to hog the lane with his bike if you would please give him some elbow room when passing. To comment, go to www.sfgate.com/chronicle/submissions/#1.